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The WebTV Plus box has been on the market for about a year and includes interactive TV functionality, while the original WebTV — also still available — does not. In addition to the ITV content, the WebTV Plus box also supports Macromedia’s Flash 2.0, Real Audio 3, Javascript, and a very limited implementation of Dynamic HTML. Java and the newer versions of RealPlayer are not supported.
In addition to delivering ITV content to Web TV Plus, Microsoft has also included ITV in Windows 98 with “WebTV for Windows 98.” This feature is latent in Win98 and will only become available when you install a TV tuner card.
Vertical Blanking Interval and Crossover Links
Mixing Web and TV content starts with the broadcaster of the TV signal. The URL and other information is encoded into the broadcast signal in the Vertical Blanking Interval (VBI) — the same part of the broadcast frequency that carries closed caption information. The WebTV Plus box recognizes this signal and responds by placing an icon in a corner of the television screen that links to the Web, representing the “crossover” link.
By clicking on this icon, the user is taken to a Web page that combines Web and TV content. For those of you without a broadcast TV station there is a way to create ITV content. The crossover link can also be embedded in a regular Web page. The link uses the following code:
This link would jump you to an ITV page where you can have mixed Web and TV content. The view=”tv” is the critical part: it ensures the WebTV Plus box knows to start using ITV content.
Embedding and Overlaying with the TV Signal
Web and television content can be mixed together in two ways.
1. A Web page can overlay the video signal so that the Web page floats over a full-screen TV signal, or
2. The TV signal can be embedded in the page like a graphic and take up only a small part of the page.
Let’s look at the code for these two options. Remember that the page in which you implement this code must have been linked to using the view=”tv” link.
Sidebar 1 The Vertical Blanking Interval contains the following information:
| Name | Definition | Example |
| URL | The web site address of the interactive TV content. | http://www.ruleweb.com |
| TYPE | A way to categorize interactive television links. | Program, Network, Station |
| NAME | The catchy or interesting message viewers see. | ABC Nightly News |
| SCRIPT | Enables the use of interactive TV links to trigger javascript functions | script:popper(“popout”) |
| EXPIRES | Specifies the last date the interactive TV link is valid | expires:19980324T023456 |
| VIEW | The view attribute specifies how the receiver should display the linked resource | view:tv |
| Abbreviations | Shortening of common names | [type:sponsor] becomes [t:s] |
| CHECKSUM | Verifies the accuracy of the string and detects data corruption. | 5EE9 |
Overlaying Code:
The TV image simply becomes the body background in the HTML; in this case, Channel 49 is shown:
Then the rest of the Web page gets built on top of the video signal. An example of this can be seen here. This will only look proper on a WebTV Plus box.
Embedding Code:
The video signal can also be used to make up an object on the page. It can be embedded much like a JPG or GIF file is placed into a Web page. Here is one example.
To embed the TV signal as an object:
To embed the TV signal as an image:
If you are in the “TV World” using ITV, the Web pages become nonscrollable so they must be designed to fit on the screen all at one time. If you want to jump back to the “Web World” to view normal Web pages, you can use this code:
WebTV has done a great job of integrating the TV signal into Web pages. Instead of creating a proprietary development platform, the company has applied Web standards in implementing interactive TV. WebTV will soon be moving onto the Windows CE operating system, which should further boost this model of convergence.
Jeff Rule is a principal at RuleWeb Development and the author of Dynamic HTML: The HTML Developer’s Guide, published this year by Addison Wesley Longman.
